Broadband offset quad-ridged waveguide orthomode transducer

The design and measurement of an offset quad-ridge waveguide orthomode transducer (OMT) are presented. The transducer comprises two orthogonal ridges inserted in a square waveguide, with one ridge offset in the propagation direction to greatly increase the single-mode operating bandwidth of the structure. Measurements of an OMT designed to operate across the 2.4-4 GHz band show a return loss of better than -20 dB for both polarisations and cross-coupling levels of below -40 dB over most of the required band.